In order to effectively mate multifiber connectors, the end portions of the plurality of optical fibers upon which one connector is mounted must generally be brought into physical contact with the end portions of corresponding optical fibers upon which another connector is mounted. Direct physical contact between the end portions of corresponding pairs of optical fibers is particularly desirable for those multifiber connectors utilized in North America since index matching gel is rarely, if ever, utilized to assist in the interconnection of the optical fibers. As such, if multifiber connectors are mated without establishing direct physical contact between the corresponding optical fibers, the signals propagating along the optical fibers may be significantly attenuated, and the reflectivity experienced by the signals may be greatly increased.
Multifiber connectors generally include a multifiber ferrule defining a plurality of bores opening through the front face of the ferrule. Multifiber connectors also include a plurality of optical fibers that extend through respective bores. In order to establish direct physical contact between the end portions of corresponding optical fibers, the end portions of the optical fibers extend beyond the front face of the ferrule defining a protrusion distance. Conventionally, the protrusion distance, measured relative to the front face is 1 μm to, at most, 3 μm. Thus, the optical fibers will generally extend beyond any imperfections in the front face of the ferrule and beyond dust, dirt or the other debris that may collect upon the front face of the ferrule.
The typical process for establishing the desired fiber protrusion beyond the front face of a ferrule begins by grinding or polishing the optical fibers and the front face of the ferrule such that the end portions of the optical fibers are flush with the front face of the ferrule. Thereafter, the front face of the ferrule and the end portions of the optical fibers are polished in such a manner so as to preferentially remove portions of the front face of the ferrule relative to the end portions of the optical fibers. Following this preferential polishing process, the end portions of the optical fibers extend beyond the front face of the ferrule by a predefined length, typically between 1 μm and 3 μm. Unfortunately, the amount by which the end portions of the optical fibers protrude beyond the front face of a ferrule is sometimes inadequate. In these instances, portions of the front faces of the ferrules of a pair of mated multifiber connectors may make contact, potentially creating a gap between the end portions of the corresponding optical fibers.
A 1 μm to 3 μm protrusion distance may initially be adequate; however, optical fiber protrusion of this magnitude may become insufficient for several reasons. For example, ferrules formed of fused quartz disposed within a thermoset or thermoplastic matrix tend to absorb moisture. The absorbed moisture, in turn, causes the ferrule to deform. This deformation is generally evidenced by cupping of the front face of the ferrule. The presence of moisture and humidity may also cause the optical fibers to somewhat withdraw into the ferrule, while correspondingly causing the front face of the ferrule to swell. If this occurs, the protrusion distance can be significantly reduced. In addition, dust, dirt or other debris may accumulate on the front face of the ferrule. Moreover, the application of mechanical loads to the optical fibers may further cause the ferrule to deform. For example, a spring load of two pounds placed across twelve optical fibers may cause the front face of the ferrule to deform by about 4 μm relative to the end portions of the optical fibers. The protrusion distance may be lessened to the point of preventing fiber-to-fiber contact as a result of the combined effects of the cupping and swelling of the front face of the ferrule, the partial withdrawal of the optical fibers into the ferrule, the accumulation of dust, dirt or other debris upon the front face of the ferrule, and the loads placed upon the optical fibers. The end portions of the optical fibers may therefore be separated or spaced from one another, thereby undesirably increasing the attenuation and reflectivity experienced by the signals transmitted via the optical fibers.
These problems are exacerbated as the area of the potential contact region between the front faces of the mated ferrules, i.e., the area across which the front faces of the mated ferrules would make contact in the absence of fiber protrusion, increases. In this regard, the problems are exacerbated since more opportunities are provided for the disadvantageous accumulation of dust, dirt or other debris in the area of the potential contact region. The issues with respect to the accumulation of dust, dirt or other debris are particularly problematic in instances in which the potential contact region includes the guide pin holes since a greater percentage of dust, dirt and other debris accumulates about the guide pin holes than upon other portions of the front face of the ferrule. Additionally, if the potential contact region is a large area, the undesirable effects of ferrule deformation and swelling as a result of exposure to moisture and humidity are increased. Moreover, the force applied to the optical fibers that urges the optical fibers into contact may be diminished in instances in which the front faces of the mated ferrules make contact across a relatively large area.
In order to establish physical contact between corresponding optical fibers of a pair of mated multifiber connectors, the end portions of the optical fibers must not only protrude beyond the front face of the respective ferrule, but must also be relatively co-planar, i.e., the end portions of the optical fibers of each respective mating part must generally lie within the same plane. Conventional processes are generally unable to establish co-planarity any closer than about 250 nm, causing a variance in the protrusion distance. As will be apparent, as the variance in protrusion of the fibers increases, the difficulty in establishing direct physical contact between the end portions of each corresponding pair of optical fibers also increases.
Each optical fiber includes a core surrounded by a cladding. As a result of the germania dopant in the core, the core is oftentimes preferentially etched relative to the cladding, particularly in instances in which the end portions of the optical fibers are polished with relatively coarse abrasive particles. The preferential etching of the core with respect to the cladding causes core dip that further reduces the likelihood of the desired fiber-to-fiber contact and, in particular, the likelihood of physical contact between the cores of the corresponding pairs of optical fibers. The failure to establish physical contact between the cores of the corresponding pairs of optical fibers is particularly disadvantageous since the signals are transmitted through the cores of the optical fibers.
Multifiber connectors can suffer additional problems in instances in which the multifiber connectors are mounted upon multimode optical fibers. In this regard, the relatively coarse abrasive particles utilized in conventional processes for polishing the end portions of the optical fibers and the front face of the ferrule in order to attain the desired protrusion distance can cause or at least exacerbate core cracking of the multimode optical fibers. While some types of core cracking can be remedied by further processing, this additional processing only increases the time and cost required to fabricate the multifiber connector. Other types of core cracking cannot be corrected, however, and the multifiber connector must, instead, be scrapped.
Accordingly, it would be desirable to develop an improved ferrule assembly in which the protrusion distance increases the likelihood that direct physical contact will be established between the end portions of corresponding optical fibers of a pair of mated multifiber connectors. Likewise, it would be desirable to develop more efficient, precise and repeatable methods for fabricating ferrule assemblies having highly protruding optical fibers with consistent coplanarity. Moreover, with respect to connectors mounted upon a plurality of multimode fibers, it would be desirable to develop an improved process for fabricating the connectors to reduce the incidence of core cracking.